In the following year, we propose to carry on research along the following lines: 1. Treatment of primates (Squirrel Monkey) with H3-Thymidine to show the possible turnover of olfactory neurons in these animals. 2. Pulse labeling of sexually mature mice with H3-Thymidine at different times in the 24 hours, followed by quantitative counts of the labeled cells, to provide evidence of a consistent mitotic daily rhythm. 3. Surgical crossing of the olfactory nerve in frog (can be technically achieved) to trace the course of the crossed nerve in the bulb and its distribution in the glomeruli by means of labeled amino acids. We will investigate if the distribution repeats the normal pattern, or if it is limited to any part of the bulb. Quantitative estimate of the synaptic apparatuses will be performed in normal reinnervated olfactory glomeruli in mice. We intend to establish if the reinnervation provides the centres with a quantitatively normal component of afferents, of if quantitative differences exist which could be eventually also detected by behavioral studies. BIBLIOGRAPHIC REFERENCES: Graziadei, P.P.C. 1974. The olfactory organ of vertebrates. A survey. In: Essays on structure and function in the nervous system. R. Bellairs & E.G. Gray (eds). Oxford, Clarendon Press.